The slotted stators cause difficult windings, require a lot of time on winding operations, and require complex and expensive coil winding equipment. Also, a structure formed of a number of teeth induces a magnetic discontinuity, to thus affect the efficiency of a motor, and generate a cogging torque depending on the presence of slots. In the case of a material such as an electric steel plate, the thickness of the electric steel plate is thick, to accordingly increase an iron loss, and exhibit the low efficiency in high-speed motors.
Many of devices that are being used in a variety of fields, including the latest technology of high-speed machine tools, air motors, actuators, and compressors, require electric motors exceeding 15,000 to 20,000 rpm, and, in some cases, electric motors that may operate at high speed up to 100,000 rpm. Almost all of the high-speed electric devices are manufactured to have a low magnetic polarity factor. This is to ensure to prevent magnetic bodies in electric devices that operate at high frequencies from having an overly excessive core loss. The main cause is due to the fact that soft magnetic bodies used in most of the motors are composed of Si—Fe alloys. In conventional Si—Fe-based materials, a loss caused by a changing magnetic field at a frequency of about 400 Hz or more may heat the Si—Fe-based materials until the materials cannot be often cooled by even any suitable cooling devices.
Until now, it has been known that it is very difficult to provide electric devices that are easily manufactured while taking the advantages of low-loss materials, at a low-cost. Most of attempts of applying the low-loss materials in the conventional devices have failed. This was due to the reason why the initial designs relied on simple replacement in which conventional alloys such as Si—Fe were replaced by new soft magnetic substances such as amorphous metal, in the magnetic cores of the devices. These electric devices show improved efficiency with low losses, from time to time, but may raise problems of causing a severe deterioration of the output, and big costs related to the handling such as molding of amorphous metal. As a result, commercial success or market entry did not occur.
Meanwhile, the electric motor typically includes a magnetic member formed of a number of stacked laminates of non-oriented electric steel plates. Each laminate is typically formed by stamping, punching, or cutting mechanically soft non-oriented electric steel plates in a desired shape. The thus-formed laminates are sequentially stacked to form a rotor or stator having a desired form.
When compared with the non-oriented electric steel plates, an amorphous metal provides excellent magnetic performance, but has been considered for a long time that it is unsuitable to be used as a bulk magnetic member such as a rotor or stator for electric motors, because of certain physical properties and obstacles that occur at the time of fabrication.
For example, the amorphous metal is thinner and lighter than the non-oriented electric steel plate, and thus a fabrication tool and die will wear more rapidly. When compared with the conventional technology such as punching or stamping, fabrication of the bulk amorphous metal magnetic member has no commercialized competitiveness due to an increase in fabrication costs for the tools and dies. Thin amorphous metal also leads to an increase in the number of the laminates in the assembled member, and also increases the overall cost of the amorphous metal rotor or stator magnet assembly.
The amorphous metal is supplied in a thin, continuous ribbon having a uniform ribbon width. However, the amorphous metal is a very mild material, and thus it is very difficult to cut or mold the amorphous metal. If the amorphous metal is annealed in order to obtain the peak magnetic characteristics, an amorphous metal ribbon is noticeably brittle. This makes it difficult to use conventional methods to configure the bulk amorphous magnetic member, and also leads to a rise in the cost. In addition, embrittlement of the amorphous metal ribbon may bring concerns about the durability of the bulk magnetic member in an application for an electric motor.
From this viewpoint, Korean Patent Laid-open Publication No. 2002-63604 proposed a low-loss amorphous metal magnetic component having a polyhedral shape and a large number of amorphous strip layers for use in high efficiency electric motors. The magnetic component may operate in a frequency range of about 50 Hz to about 20,000 Hz, while having a core loss so as to indicate the enhanced performance characteristics in comparison with the Si—Fe magnetic component that operates in the same frequency range, and has a structure that is formed by cutting an amorphous metal strip to then be formed into a number of cut strips having a predetermined length and laminating the cut strips using epoxy in order to form a polyhedral shape.
However, the Korean Patent Laid-open Publication No. 2002-63604 discloses that brittle amorphous metal ribbon is still manufactured via a molding process such as cutting, and thus it is difficult to make a practical application. In addition, the Korean Patent Laid-open Publication No. 2002-63604 discloses that the magnetic component may operate in a frequency range of about 50 Hz to about 20,000 Hz, but did not propose an application for higher frequency.
Meanwhile, in the case that a high-speed motor of a high output of 100 kW and 50,000 rpm is implemented using silicon steel plates as in drive motors for electric vehicles, an eddy current increases due to high-speed rotation, and thus a problem of generating heat may occur. Also, since the drive motors for electric vehicles are fabricated in a large size, it is not possible to apply the drive motors to the driving system of the in-wheel motor structure, and it is undesirable in terms of increasing weight of the vehicles.
In general, the amorphous strip has a low eddy current loss, but conventional motor cores that are made of laminated amorphous strips may cause it to be difficult to make a practical application due to difficulties of a manufacturing process as pointed out in the prior art, in view of the nature of the material.
As described above, the conventional amorphous strips provides superior magnetic performance compared to non-oriented electrical steel plates, but are not applied as the bulk magnetic members such as stators or rotors for electric motors because of obstacles that occur during processing for the manufacture.
In addition, the conventional method of manufacturing the amorphous soft magnetic core did not present a method of designing a magnetic core optimal in the field of an electric motor with a high-power, high-speed, high-torque, and high-frequency characteristics.
In addition, the need for improved amorphous metal motor members indicating the excellent magnetic and physical properties required for high-speed, high-efficiency electrical appliances is on the rise. Development of manufacturing methods of efficiently using the amorphous metal and practicing mass-production of a variety of types of motors and magnetic members used for the motors is required.